1. Field of the Invention
The present invention generally relates to an elevator (or lift) control apparatus and more particularly to an apparatus for performing compensation for shock which is likely to occur upon starting of the elevator car operation without resorting to the use of a car-onboard load detector
2. Description of the Prior Art
Heretofore, in the conventional elevator (or lift) systems, compensation for the shock or bouncing which the elevator car (or cage) may otherwise experience upon starting of the elevator operation (hereinafter referred to as the start compensation for convenience of explanation) has generally been achieved by making use of a signal produced by a load detector installed beneath the car (i.e. car-onboard detector), as is disclosed in Japanese Patent Application Laid-Open No. 149040/1975 (JP-A-50-149040) and Japanese Patent publication No. 2275/1975.
It is also known that the start compensation is effectuated by detecting an unbalance torque applied to a brake apparatus without using the car-onboard load detector. For particulars, reference may be made, for example, to JP-A-62-56277 and JP-A-62-116478.
Further, there is disclosed in JP-A-57-1180 a start compensation system in which a brake apparatus is provided with a brake shoe which is displaceable relative to a stationary structural member of an elevator machine house, wherein the unbalance torque is detected on the basis of the displacement of the shoe to be utilized for the elevator control.
In the technical field of the disc (or disk) brake, it is known to mount displaceably a stationary disc of the disc brake on a bracket of a base structure, wherein displacement of the stationary disc is detected by a switch adapted for detecting the actuated state of the brake, as is disclosed in JP-A-58-109741.
In the case of the conventional elevator start compensation apparatus exemplified by the one disclosed in the JP-A-62-56277, the unbalance torque applied to the brake unit is detected by a torque sensor, wherein the start compensation is performed in dependence on a detected value derived from the output of the torque sensor. To this end, it is required that the torque sensor must be able to produce the output continuously and linearly as a function of the unbalance torque. Besides, the requirement imposed on the torque sensor presents a direct influential factor for the satisfactory elevator start compensation.
Such being the circumstances, the control system inclusive of the torque sensor is necessarily very complicated and expensive, which is a disadvantage.